1. Field of the Invention
This invention relates to semiconductor processing techniques. Specifically, the present invention relates to a processing technique for providing an enhanced barrier between a semiconductor substrate and a metallized contact.
2. Prior Art
Electrical connections to semiconductor devices formed in a semiconductor substrate are typically made using metallized contacts. In a standard process, metallized contacts are created by first forming a depression, referred to as a contact well, through an undermetal dielectric which overlies the semiconductor substrate and semiconductor devices formed thereon. The contact well is formed directly above the region to which electrical connection is to be made. For example, the contact well may extend clown to a polysilicon line or even completely down to the semiconductor substrate to allow for direct electrical connection to a source or drain of a semiconductor device. Next, in an evacuated or low-pressure environment, a layer of conductive material such as platinum is sputtered over the undermetal dielectric covered substrate including the contact well. After the sputtering step, the semiconductor wafer, that is, the semiconductor substrate and all overlying materials, is removed from the low-pressure environment and placed in a furnace at an increased or atmospheric pressure. This step is referred to as a sinter. The sinter causes the platinum to react with the portion of the semiconductor substrate exposed in the contact well. The reacted platinum and exposed semiconductor substrate form a platinum silicide within the contact well. The platinum which is disposed on top of the undermetal dielectric, on the other hand, does not react during the sinter process.
Unfortunately, movement of the wafer from the low-pressure environment to the oven for the sinter is extremely time-consuming. In order to safely perform a vacuum break, that is, a transition from a low-pressure environment to a much higher pressure environment, the pressure must be very meticulously and slowly changed. An abrupt or rapid change in pressure creates turbulence which in turn may disrupt dust or other contaminating particles within the low-pressure environment. If the disrupted particles contact the semiconductor devices, shorts or defects in the devices may result. Therefore, any changes in pressure must be gradually and gently carried out. As a result, the movement of the wafer from the low-pressure sputter environment to the much higher pressure oven environment must be performed over an extended period of time.
In the typical metallized contact formation process, following the sinter, an etch step such as, for example, an aqua regia strip using a combination of nitric and hydrochloric acid is used to remove the unreacted platinum remaining on top of the undermetal dielectric. The platinum silicide, or reacted platinum, is not affected by the aqua regia strip and, thus, remains intact within the contact well.
Due to the nature of the platinum silicide, no oxidation of the silicide occurs while the wafer is exposed to air during the aqua regia strip. Therefore, the platinum silicide does not provide a barrier over the contact well. That is, if the layer of electrically conductive material used as the conductor in the metallized contact is placed on top of the platinum silicide, unwanted diffusion of the conductor material through the silicide and into the semiconductor substrate will occur. To provide a sufficient diffusion barrier between the contact well and the conductor material, the wafer is returned to the low-pressure sputter environment and a metallic barrier layer is sputtered over the undermetal dielectric and the contact well containing the platinum silicide.
Commonly, the wafer is then subjected to another vacuum break and is exposed to air at atmospheric pressure. In so doing, an oxide is formed on the metallic barrier layer. The oxidized metallic barrier layer is intended to prevent diffusion of the conductor material into the semiconductor substrate.
Next, the wafer is again returned to the low-pressure environment and the layer of conductor material is sputtered over the oxidized metallic barrier layer. The layer of conductor material is then covered with a protective coating. After completion of the above-described steps, formation of the metallized contacts is completed. The wafer then undergoes additional process steps including inter-metal oxide deposition steps, wherein the fabrication of the semiconductor devices on the semiconductor substrate is completed.
As set forth above, conventional metallized contact formation techniques require numerous process steps involving several vacuum breaks. Unfortunately, each of the process steps required in the formation of the metallized contacts has a cost associated therewith. Thus, the cost of a metallized contact manufactured using conventional formation techniques is compounded by the numerous process steps. Additionally, due to the amount of time required for each vacuum break, wafer throughput is significantly reduced. Furthermore, the numerous process steps and required transportation of the wafer from one environment to another necessitates repeated wafer handling. As a result, defects associated with wafer handling are also prevalent in wafers having contacts formed using conventional metallized contact formation techniques.
Thus, the need has arisen for a metallized contact, and a method for forming such a contact, which reduces the amount of required process steps, does not require numerous vacuum breaks, and eliminates the need for substantial wafer handling.